The invention relates to an improved method of manufacturing clad thermocouple cable consisting of a first preferred metal sheath surrounding the thermocouple wires and insulating material, either in powered form or as pellets threaded along the wire, wherein the metal sheath has a longitudinally welded seam further surrounded by an outer protective second sheath.
The making of thermocouple cables by placing an insulating material and the thermocouple wires inside of a sheath and the subsequent drawing down of the sheath to form the final desired diameter of cable/wire has been accomplished both through the use of tubing and subsequently by the use of longitudinally and/or spirally rolled and welded metal strips as sheathing material. The difficulty in the use of strips of metal sheathing and then either spirally or longitudinally rolling them around the insulating material and thermocouple wires has been in creating a continuous uninterrupted final welded seam that does not contain discontinuities resulting in detrimental diffusion between the thermocouple cable and its surounding environment through the welded seam. Further the materials used to clad the insulating material and thermocouple wires are usually designed for a specific purpose or coatings are applied to the strip to be used as the cladding material to provide a resistance barrier and as such the material or coating are expensive to use and/or apply. Any discontinuities in the welding of the seam are detrimental to the operation and longevity of the resulting thermocouple cable and defeat the purposes for the use of the expensive cladding material or for the application of the barrier coatings.